Zusammenfassung
The deep time-varying meridional overturning circulation (MOC) in the
Indian Ocean in the German "Estimating the Circulation and Climate of
the Ocean" consortium efforts (GECCO) ocean synthesis is being
investigated. An analysis of the integrated circulation suggests that,
on time average, 2.1 Sv enter the Indian Ocean in the bottom layer
(>3200m) from the south and that 12.3 Sv leave the Indian Ocean in the
upper and intermediate layers (<1500 m), composed of the up-welled
bottom layer inflow water, augmented by 9.6 Sv Indonesian Throughflow
(ITF) water. The GECCO time-mean results differ substantially from those
obtained by inverse box models, which being based on individual
hydrographic sections and due to the strong seasonal cycle are
susceptible to aliasing.
The GECCO solution shows a large seasonal variation in its deep MOC
caused by the seasonal reversal of monsoon-related wind stress forcing.
The associated seasonal variations of the deep MOC range from 7 Sv in
boreal winter to 3 Sv in summer. In addition, the upper and bottom
transports across the 34 S section show pronounced interannual
variability with roughly biennial variations superimposed by strong
anomalies during each La Nina phase as well as the ITF, which mainly
affect the upper layer transports. On decadal and longer timescale, the
meridional overturning variability as well as long-term trends differs
before and after 1980. GECCO shows a stable trend for the period
1960-1979 and substantial changes in the upper and bottom layer for the
period 1980-2001.
By means of an extended EOF analysis, the importance of Ekman dynamics
as driving forces of the deep MOC of the Indian Ocean on the interannual
timescale is highlighted. The leading modes of the zonal and meridional
wind stress favour a basin-wide meridional overturning mode via Ekman
upwelling or downwelling mostly in the central and eastern Indian Ocean.
Moreover, tropical zonal wind stress along the equator and alongshore
wind stress off the Sumatra-Java coast contribute to the evolution of
the Indian Ocean dipole (IOD) events. (C) 2012 Elsevier B.V. All rights
reserved.
